A driving mechanism, such as a motor or engine, can generate driving motions at a mechanism output, such as at a rotatable output shaft. The output shaft can, for example, provide a rotational kinetic motion to another piece of equipment via a rotatable drive shaft connected to the output shaft. The piece of equipment receiving the rotational kinetic motion can utilize the driving rotational motion as an energy source to operate. In one example configuration, a gas turbine engine, also known as a combustion turbine engine, is a rotary engine that extracts energy from a flow of combusted gases passing through the engine onto a multitude of turbine blades. The gas turbine engine can provide at least a portion of the rotational kinetic motion to rotating equipment, such as an accessory gearbox, where the rotational motion is utilized to power a number of different accessories. The accessories can include generators, starter/generators, permanent magnet alternators (PMA) or permanent magnet generators (PMG), fuel pumps, and hydraulic pumps.
A planetary gear system can be utilized to drive one or more of the accessories including the starter by fitting a gear train of the starter within a compact profile envelope. Planetary gear systems include one or more planet gears meshed between input and output gears, where the planet gears are designed to rotate about their own axes and to orbit about another axis in the gear train.